The present invention relates to a process for the preparation of silacycloalkanes. The described process uses an alkylaluminum hydride to reduce halosilacycloalkanes to silacycloalkanes. In an additional embodiment of the instant invention, the halosilacycloalkane is added to the alkylaluminum hydride and the silacycloalkane product is immediately vacuum distilled from the mixture. The process, as described, provides high yield of silacycloalkane product.
Silacycloalkanes have been found to be useful in producing hydrogenated films with a silicon and carbon backbone. These films are known to exhibit very low dark conductivity at room temperature and to show good corrosion resistance. The small, strained, organosilicon ring is known to make silacyclobutanes highly reactive, particularly with nucleophilic and electrophilic reagents. As a consequence of the unique chemistry of silacycloalkanes, few methods for their production have been reported.
Laane, J. Am. Chem. Soc. 89:1144, 1967, appears to be the first to describe a process for the preparation of silacycloalkanes. Laane prepared 1,1-dichloro-1-silacyclobutane by adding 3-chloropropyltrichlorosilane dropwise to ethyl ether, containing magnesium powder. The 1,1-dichloro-1-silacyclobutane, in n-butyl ether, was added dropwise to lithium aluminum hydride, in n-butyl ether, to form the reduced silacyclobutane. The addition was completed over a five-hour period, with the reaction mixture maintained at a temperature of -5.degree. C. to +5.degree. C. After 10 hours, the reaction was allowed to progress at room temperature and after 24 hours the mixture was distilled. The reported yield of product was 46%.
Silicon-hydrogen compounds can be prepared by reduction of silicon halides, partially halogenated silanes, or organohalogen silanes, in the presence of metal catalysts, such as aluminum, magnesium, and the like. The use of hydrides such as LiAlH.sub.4 or AlH.sub.3, has also been proposed for this purpose. Jenker, U.S. Pat. No. 3,100,788, issued Aug. 13, 1963, described a process for adding hydrogen to halogenated organosilanes by employing an alkali metal or alkali hydride in a hydrogen atmosphere.
Robinson, U.S. Pat. No. 3,499,020, issued Mar. 3, 1970, describes a process for reducing compounds of the type "R.sub.n SiX.sub.4-n, where R is hydrogen, alkyl, cycloalkyl, alkenyl, aryl, or alkaryl and X is halogen, --NR'.sub.2, or an oxygen-bearing group." The process described by Robinson uses a reducing agent conforming to the formula "R.sub.2 AlH, where R is an alkyl radical." The reducing agent is diluted in a solvent and the process is run at atmospheric pressure.
Schulz, Co-pending U.S. Application 07/516,599, filed June 1, 1980 describes a process for reducing organohalosilanes and volatile organohalopolysilanes with liquid alkylaluminum hydride. The Co-pending Schulz application does not describe the reduction of silacycloalkanes. The reactive nature of the silacycloalkane ring makes these materials unique in relation to the organohalosilanes and volatile organohalopolysilanes described in the Co-pending Schulz patent application, and cited prior publications.